Various fibrous structures having a high moisture absorptive and desorptive property have been proposed already. For example, in the Japanese patent laid-open No. 11/247069, there is proposed a cloth having fine particles of a highly moisture absorptive and desorptive organic substance on the cloth. However, in such a cloth, a means for fixing the highly moisture absorptive and desorptive organic fine particles on the surface of the fiber is necessary and, further, in the highly moisture absorptive and desorptive organic fine particles, a cross-linking structure is introduced into fine particles of acrylonitrile by hydrazine whereby it is colored in light pink color to light brown color and degree of whiteness of the cloth is poor. In the Japanese patent laid-open No. 2001/30,402, there is proposed a water absorptive and moisture absorptive cloth using a highly water absorptive and moisture absorptive fiber where the difference in moisture absorptive ratios between 20° C. at 60% RH and 20° C. at 97% RH is 30% or more and the water absorptive amount per unit fiber is 300% by weight to 8000% by weight. However, in such a cloth, a highly water absorptive and moisture absorptive fiber where the water absorptive amount per unit fiber is 300% by weight or more is used and, therefore, the area where water is absorbed has a sticky feeling and there is a problem that, in order to solve the above, it is to be made into a two-layered structure.
It has been also known that the hue is from light pink color to light brown color in a moisture absorptive and desorptive fiber of an acrylic acid type which is subjected to introduction of cross-link by a hydrazine compound into an acrylic fiber followed by hydrolysis and, if necessary, subjected to introduction of carboxyl group of a metal salt type by means of neutralization. Accordingly, the fibrous structure where such a moisture absorptive and desorptive fiber of an acrylic acid type is blended keeps the hue of the fiber as it is whereby it is not suitable for white things. In addition, a fibrous structure where a moisture absorptive and desorptive fiber of an acrylic acid type and cotton are blended is usually bleached with hydrogen peroxide, sodium chlorite or the like for removing cotton dust and fat/oil coming from the starting material for the cotton. However, there is a problem that, as a result of such a treatment, the hue of the moisture absorptive and desorptive fiber of an acrylic acid type becomes darker and, therefore, the use has been limited. Further, a fibrous structure where a moisture absorptive and desorptive fiber of an acrylic acid type and wool are blended is usually subjected to a bleaching treatment with a reducing agent for removing fat/oil, etc. coming from the starting material for wool and making white. However, there is a problem that, although color of the moisture absorptive and desorptive fiber of an acrylic acid type becomes light by such a treatment, the stability is poor and the color returns to pink or light brown by washing whereby that does not satisfy the requirement for white color especially in the field of clothing.
As a method for solving such problems, there have been known a method where the original hue of the moisture absorptive and desorptive fiber of an acrylic acid type is covered by means of dyeing and a method where the moisture absorptive and desorptive fiber of an acrylic acid type is subjected to a reversible knitting inside. However, those methods are for colored things anyway and are not suitable for the need of white things.
In addition, there have been disclosed some methods where original hue of the moisture absorptive and desorptive fiber of an acrylic acid type is improved. For example, since a moisture absorptive and desorptive fiber of an acrylic acid type prepared by a method of the Japanese patent laid-open No. 05/132,858 shows dark pink color to dark brown color, there is a disadvantage that its use is limited and, in the invention of the Japanese patent laid-open No. 09/158,040 proposed for overcoming the disadvantage, there is disclosed that an acid treatment A is conducted after a cross-linking treatment with a hydrazine compound and that an acid treatment B is conducted after a hydrolyzing treatment with an alkali whereby a considerable improvement in whiteness is achieved. However, even by such a technique, there is still a problem that the moisture absorptive and desorptive fiber of an acrylic acid type is colored in bleaching said fiber blended with cotton. In the Japanese patent laid-open No. 2000/303,353, there is disclosed that, as a method for improving the whiteness of a moisture absorptive and desorptive fiber of an acrylic acid type, a hydrolyzing treatment is carried out in an oxygen-free atmosphere. However, even in such a method, the resulting fiber is colored upon bleaching treatment and repeated washing and, therefore, it is the current status that a disadvantage of poor stability in whiteness still remains. Accordingly, even in a moisture absorptive and desorptive fiber of an acrylic acid type having an improved original hue, that is not still in a level of being durable to bleaching and to reducing treatment when made into a blended fabric.